Boron compounds have been used for the treatment of cancer through .sup.10 B neutron capture therapy (BNCT). Various derivatives of dodecahydrodecaborate [B.sub.12 H.sub.12 ].sup.2- and decahydrodecaborate [B.sub.10 H.sub.10 ].sup.2- have been synthesised. The sulphydryl-containing borane anion [B.sub.12 H.sub.11 SH].sup.2- (BSH) has been found to be a most suitable species for the treatment of glioma by BNCT. It is found that BSH is preferentially taken up by the brain cancer tumour (glioma), which allows selective targeting of thermal or epithermal neutrons. Presently, there is no treatment for glioma and early death of the patient is to be expected.
The compound BSH has been known for some time and is approved for therapy in the USA. A number of syntheses of BSH have been reported in the literature (W. H. Knoth, J. C. Sauer, D. C. England, W. R. Hertler and E. L. Muetterties, J. Am. Chem. Soc., 1964, 86, 3973; E. I. Tolpin, G. R. Wellum and S. A. Berly, Inorg. Chem., 1978, 17, 2867; T. Nakagawa, T. Yoshizaki and K. Aono, J. P. Kokai 75 92897 C.A. 1976 84: 79701v; M. Komura, K. Aono, K. Nagasawa and S. Sumimoto, Chem. Express, 1987, 2, 173; V. A. Brattsev and O. R. Sagitullin Pat. USSR 1328290 (1987) C.A.; 1987, 107: 179481k). However, these synthetic methods are complicated and generally involve many synthetic steps. Certain of the intermediate products may be toxic, which leads to purification problems. Finally, the overall yields are generally poor. All syntheses start from the dodecahydrododecaborate anion [B.sub.12 H.sub.12 ].sup.2- which can be obtained in high yield when decaborane is treated with triethylamine-borane (N. N. Greenwood and J. H. Morris, Proc. Chem. Soc., 1963, 338.) B.sub.10 H.sub.14 +2Et.sub.3 NBH.sub.3 .fwdarw.[Et.sub.3 NH].sub.2 [B.sub.12 H.sub.12 ]+3H.sub.2.
Alternatively, it can be obtained by the reaction: 10BH.sub.3 SMe.sub.2 +2NaBH.sub.4 .fwdarw.Na.sub.2 [B.sub.12 H.sub.12 ]+10SMe.sub.2 +13H.sub.2 (H. C. Miller, N. E. Miller and E. L. Muetterties, Inorg. Chem., 1964, 3, 1456; W. V. Hough, C. R. Guibert, and G. T. Hefferan, U.S. Pat. No. 3,961,017. C.A. 1976, 85, P126732V).
In the best reported synthesis (Komura et al., see above) seven steps are involved in converting this compound to Na.sub.2 [B.sub.12 H.sub.11 SH]. The overall yield is 68% though in practice this may represent a maximum rather than a routine achievable yield.
The syntheses of the [B.sub.12 H.sub.11 SCN].sup.2- anion, as salts with the cations [Et.sub.3 NH].sup.+, [Et.sub.4 N].sup.+, [(Ph.sub.3 P).sub.2 N].sup.+, Na.sup.+, or Cs.sup.+, are more efficient than earlier reported preparations (e.g. H. -G. Srebny and W. Preetz, Z. anorg. allg. Chem., 1984, 513, 7). Previously reported methods require the inconvenient prior preparation of (SCN).sub.2 from Pb(SCN).sub.2 and Br.sub.2, and the use of [Bu.sub.4 N].sub.2 [B.sub.12 H.sub.12 ] in CH.sub.2 Cl.sub.2. The methods of the present invention conveniently start from simple thiocyanate salts, and easily synthesised salts of [B.sub.12 H.sub.12 ].sup.2- with the cations [Et.sub.3 NH].sup.+, Na.sup.+, or K.sup.+. The reactions may also be carried out in aqueous solutions and provide quantitative yields. The compound, as its sodium salt, has excellent potential for neutron capture therapy, in view of its low biological toxicity, and good tumour-localising properties in a tumour model system.
The synthesis of the 1,7-isomer (and the 1,12-isomer as a small byproduct) of salts of [B.sub.12 H.sub.11 (SCN).sub.2 ].sup.2- have not been reported previously. Such compounds are also believed to have potential for neutron capture therapy.